After successfully completing this lesson you will have acquired the basic
theoretical knowledge and skills needed to confidently purge the cofferdam on
aphromoo pump to gain maximum benefit from this lesson
you should successfully have completed the previous lesson this lesson gives
step-by-step instructions on how to purge the cofferdam of a pump the
practical section consists of two parts first there is a demonstration of the
procedure this is followed by an interactive guided walkthrough of the
same procedure
purging the cofferdam at regular intervals is an important precaution
against malfunctions and unexpected shutdowns this procedure helps you
detect any leakages through the cargo or hydraulic oil seals you can monitor the
condition of the shaft seal system and plan the maintenance of the pump on the
basis of results observed you will now see a demonstration of the
cofferdam purging procedure click on place a suitable container underneath
the exhaust trap vent line to collect any leakage check that the drain valve
and the bottom of the exhaust trap are not clogged with residue after the last
purging operation ensure that the drain valve is closed
check that the relief valve on the hydraulic control valve is open connect
the air or nitrogen supply hose to the snap-on coupling on the purging
connection remember to drain the supply hose of any condensed water before
connecting it to the snap-on coupling open the valve on the air or nitrogen
supply line check that there is air or nitrogen coming out of the exhaust trap
vent line the relief valve is set to an opening
pressure of 3 to 3.5 bar so a small air or gas leakage here is normal to stop
purging close the valve on the air or nitrogen supply line move the container
underneath the exhaust trap drain valve disconnect air or nitrogen supply close
the exhaust trap drain valve measure the amount of leakage evaluates
and log the purging result this completes the demonstration of the
cofferdam purging procedure in order to maintain a complete understanding of the
condition of a pump cofferdam both purging procedures and systematic
assessment of results are required as a general rule the cofferdam should be
purged as shown in this table note neglecting purging can result in a
blocked cofferdam
the purging form should be filled in with the results from every purging
operation each horizontal line in the form represents one cargo in one tank
from loading through to discharging if a ship loads and discharges some tanks
more frequently than others an extra form should be filled in for these tanks
completed purging form to be sent to the ship owner and to fram-o
the green copy is for the ship the red copy for the ship owner and the white
copy for fram-o results can also be sent to fram-o
in electronic format at purging at fram-o
dot n o the ship staff has the primary responsibility for purging and any
subsequent action necessary in case the ship staff need further information or
advice contact fram-o cargo in the cofferdam can come from the shaft seals
flange face seals in the pipe stack or pump unit or damage such as cracks on
the pipe stack pump unit or cofferdam pipe a small leakage rate over the shaft
seals up to about 0.5 liters per day during pump operation is normal and
replacement of seals should not be necessary with this leakage rate for
short periods of time higher leakage Peaks can occur the leakage rate also
depends on the type of cargo some cargoes liked naphtha condensate etc
penetrate the shaft seals more easily than lube oils vegetable oils and other
viscous cargoes if the leakage rate is up to about 2 liters per day the pump
must be purged a couple of times daily and inspected / pressure tested as soon
as possible to find the reason for the leakage intensified the purging if the
leakage rate is increasing above acceptable level if this is not keeping
the leakage under control do not operate the pump use the portable pump to
discharge the cargo the development of a cargo leakage can be followed if purging
is done according to specified intervals maintenance work can be planned
accordingly and unexpected shutdown due to leakage can be avoided hydraulic oil
in the cofferdam can come from the mechanical seal flange face seals in the
pipe stack or pump unit or damage such as cracks on the pipe stack will pump
unit a small leakage rate into the cofferdam up to
about 10 milliliters per hour or 0.25 liters per day from the mechanical oil
seal or lip seal during pump operation is normal for short periods of time
higher leakage Peaks can occur if the leakage rate is increasing above
acceptable level the pump must be purged a couple of times daily and inspected /
pressure tested as soon as possible to find the reason for the leakage
intensify the purging if the leakage rate is increasing above acceptable
level if this is not keeping the leakage under control do not operate the pump
use the portable pump to discharge the cargo